In one word, no. I've found them very reliable if they are kept up. It's not a car to let routine maintenance slip on. However, the newest one is now 8 years old so those saying they are not reliable will eventually be right. However, they may miss out on 15 or 20 years of fun waiting to be right.

Here's a link to a discussion of M5 longevity and reliability that I posted on the M5board.